1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to updating a revocation list and reproducing encrypted content, and more particularly to a method of updating a revocation list including at least one revocation entity, a method of updating a revocation list between devices in an off-line state, a method of enabling or disabling reproduction of encrypted content on the basis of a revocation list, and apparatuses therefore.
2. Description of the Related Art
In recent years, the amount of digital content has drastically increased, and thus demands for digital rights management (DRM) technologies are rapidly increasing. DRM may be defined as a technology for preventing illegal copying of content in the narrow sense, but, in the broad sense, DRM may be an umbrella term that encompasses technologies and service systems for ensuring transparency and reliability over the entire life cycle of the digital content. That is, DRM may be a technology and a service system that manage intellectual property rights and ensure a transparent and reliable distribution environment over the entire life cycle of the digital content. DRM services have different definitions and ranges according to venders. International Data Corporation (IDC) provides a definitive explanation of DRM services as “software and services used over the entire life cycle of the digital content from creation and distribution of the digital content to consumption thereof”. IDC classifies various uses of DRM into four representative uses.
First, DRM is used to protect the commercial value of digital content by preventing illegal copying.
Secondly, DRM is used to protect content secrecy in terms of document security between enterprises or within an enterprise.
Thirdly, DRM is used to protect intellectual property rights for content such as treatises, photographs and novels that are not for sale.
Fourthly DRM may be used to ensure integrity of digital content without modification, damage and correction during a distribution process.
In selling or distributing the content, a situation where reproduction or redistribution of sold content must be blocked occurs even after the selling of the content is completed. For example, the use of distributed content must be prohibited if the distributed content is associated with social problems or arbitrary publicity of a specific product. Also, if the content distributed using DRM in a free trial period is used without authorization through DRM hacking, the permission or authorization to use the corresponding content must be collectively revoked. However, in the case of general DRM being currently used, once purchase of content is completed, it is difficult to restrict the use of the corresponding content. Thus, there are DRM solutions for providing revocation functions. However, these DRM solutions have limitations in that whenever the content is reproduced, it must be checked whether reproduction of corresponding content is enabled only through network communication. For this reason, conventional DRM solutions are limited by a device, and are useless in an offline state.